1. Field of the Invention
The present invention relates to an ink composition for use in electrophotography, electrostatic printing and electrostatic recording, or for use in printing inks in general use, ink-jet printing inks, and paints; and a recording method using the ink composition by electrically charging the ink composition and ejecting the ink composition onto an electrically charged substrate.
2. Discussion of Background
In ink-jet recording systems in general use, a liquid or solid ink is ejected from a nozzle, a slit or a porous film and caused to impinge upon a sheet of paper, cloth or film to perform recording thereon.
Ink-jet printers are in general use because of the advantages over other printers that noise generated while in use is much smaller, the size thereof is more compact and the cost thereof is lower in comparison with other printers.
Furthermore, as a result of recent intensive research and development activities in this field, single-color ink-jet printers capable of printing black images with high quality on plain paper such as writing-paper and copy papers are also commercially available.
Examples of a recently proposed wet-type toner jet recording system are as follows:
(1) A printing system which applies a voltage with the same polarity as that of toner particles to a tip of a line head to produce an aggregate of the toner particles, and eject the aggregate therefrom for printing (PCT/AU92-00665); and PA1 (2) A printing system comprising a toner ejecting means, which is disposed near a development roller and an electrophotographic photoconductor with a development gap therebetween and deposits a wet toner from the surface of the development roller on latent electrostatic images formed on the photoconductor.
U.S. Pat. No. 3,060,429 discloses an electrostatic ink-jet printing system which electrostatically attracts a development liquid serving as an ink. This system comprises two pairs of electrodes, one pair being opening and closing electrodes for intercepting or controlling the jet flow of ink droplets, and the other pair being electrodes for adjusting the path of the ink-droplet ejection, and includes the steps of generating charged ink droplets, accelerating the ejection of the ink droplets from a nozzle which holds the ink therein towards a plate-shaped electrode, with the application of a high voltage between the nozzle and the plate-shaped electrode, and supplying ink droplets to a sheet of paper which is disposed in front of the plate-shaped electrode immediately before the ink droplets reach the plate-shaped electrode.
It is desired that an ink for use in an ink-jet printer satisfy the following requirements: (1) capable of forming images on paper, without image spreading and fogging, with uniformly high resolution and image density; (2) causing no clogging at a tip of an ink-ejection nozzle and constantly providing excellent ink-ejection response and stability; (3) having excellent drying characteristics on paper; (4) capable of forming images with high fastness; and (5) having excellent long-period preservation stability.
In order to meet these requirements, various studies have been made with respect to ink-jet printing inks, including studies on various additives and water-soluble organic solvents for use in ink-jet printing inks.
Japanese Patent Publication 62-11781 discloses various surfactants for an ink-jet printing ink; and Japanese Laid-Open Patent Application 1-25789 discloses the use of a block copolymer of ethylene oxide and propylene oxide for use in an ink-jet printing ink.
Furthermore, in a wet-type toner for use in conventional ink-jet printing systems, as a carrier medium for the wet-type toner, isoparaffin is mainly used; and as a coloring agent therefor, for instance, carbon black and organic pigments are used.
Conventional dry-type developers for use in electrophotography are generally prepared by kneading a coloring agent, a resin and a charge-controlling agent, and pulverizing the kneaded mixture to finely-divided particles with a particle size in a range of 5 to 10 .mu.m.
Conventional wet-type developers for use in electrophotography are generally prepared by dispersing a non-aqueous resin dispersion and a coloring agent to prepare a dispersion of toner particles with a particle size in a range of 0.5 to 2 .mu.m. Generally wet-type developers are capable of providing clearer images than dry-type developers.
When such a wet-type developer for use in electrophotography is prepared, a non-aqueous resin dispersion is employed in order to disperse a coloring agent such as a pigment in a solvent. As a resin for such a non-aqueous resin dispersion, an amphiphatic resin is generally used.
Such an amphiphatic resin is derived from a vinyl polymer, and as such amphiphatic resin, a graft polymer is mainly used. The use of such graft polymer, however, has the problems that when the graft polymer is produced, a relatively large amount of an ungrafted polymer, which is soluble in a non-aqueous solvent, is produced as a side product, and the dispersibility of a coloring agent is impaired by the thus produced ungrafted polymer, resulting in that precipitations are eventually formed in the course of a long-period preservation of the developer.
There have been proposed various non-aqueous resin dispersions for use in liquid developers for developing latent electrostatic images formed in electrophotography or for use in paints, and methods of producing such non-aqueous resin dispersions.
For instance, Japanese Patent Publication 62-3859 discloses a liquid developer for use in electrophotography comprising toner particles made of a resin which is prepared by allowing a natural-resin-modified thermosetting resin to react with a long-chain alkyl-group-containing monomer.
Such a non-aqueous resin dispersion is effective for improving the dispersion stability of a coloring agent, but does not have sufficient dispersion stability.
Japanese Patent Publication 56-10619 discloses a liquid toner which is prepared by the steps of synthesizing white latex particles with a size of 0.4 to 0.8 .mu.m in a non-aqueous solvent and dyeing the white latex particles with a dye such as Victoria Blue. This method, however, has the shortcomings that it is difficult to prepare a black toner and that the toner produced by this method is of a dye type and therefore images formed by the toner have low image density and low light resistance and fade easily when exposed to light.
An ink for ink jet printing which satisfies all of the previously mentioned five requirements has not yet been produced.
Several ink jet printers capable of producing full color images, are commercially available. However, when plain paper is used for the printing, faithful image reproduction cannot be performed by those ink jet printers because the drying performance of the inks for use with the printers are insufficient, high speed reproduction output cannot be attained, and inks with different colors tend to be mixed during full-color image formation.
Therefore, it is usually necessary that a special surface-treated paper be used for these printers, so that the printing cost is high and it is difficult to spread these printers for general use.
Conventional ink jet printing systems using a wet toner which contains an organic solvent have the shortcomings that the application of high voltage is required to eject the wet toner from an ejection head or from the surface of a development roller; the fixing performance of the ejected wet toner to a printing paper is poor; the obtained image density is low; and high image resolution is difficult to obtain.